Hubbard Model for Asymmetric Ultracold Fermionic ... - KOMET 337

4 CHAPTER 1. INTRODUCTION1.2 Unbalanced Fermi-mixtures: a brief experimental overviewIn this section we present the experimental motivation for analyzing unbalanced Fermimixtureson optical lattices. In recent experiments [16] [17] the superfluidity of two-componentunbalanced Fermi-mixtures has been examined experimentally. Here we show brieflythe results obtained in the experiment done at Rice university [16]. In this experiment twocomponentFermi-mixtures with different proportions of the components were cooled downbelow the critical temperature of the superfluid phase transition. With the help of in-situimages, the spatial distribution of the majority and of the minority species were imaged. Theresults are shown graphically here:Figure 1.2: In-situ images of the spatial particle distributions are represented here. In the leftimage the population of the minority cloud is decreased from (a) to (f), while the temperatureis constant. In each part the upper picture shows the distribution of the majority species,the middle picture shows the distribution of the minority species and the lower picture showstheir difference. In the right image the parts (a)/(b) and (c)/(d) are measured at differenttemperatures. The parts (a) and (b) correspond to the lower temperature, which is the sameas in the left image. The parts (c) and (d) are measured at a higher temperature, but stillbelow the critical temperature of the superfluid phase transition.From Figure 1.2 we conclude that:- There is superfluidity in unbalanced Fermi-mixtures at low temperatures.- Phase separation takes place.- A superfluid core with balanced occupation is in the middle of the trap.- In the outer region we find the unpaired part of the majority cloud.- There is a second critical temperature beyond the superfluid-to-normal critical temperature.Between those critical temperatures we find a polarized superfluid phase.Hence, unbalanced Fermi-mixtures differ from balanced ones, where we find only one criticaltemperature and no phase separation, since the complete cloud is superfluid below the critical